A joint announcement from the American Meteorological
Society
and Northern Illinois University

Researchers track Illinois storm damage
to crops via NASA satellite

Researchers say they used data produced by a NASA satellite
orbiting more than 400 miles above the earth to estimate the
cost of crop damage from hail and wind storms that swept through
west-central Illinois, the heart of America's farmlands.

"This could become the preferred method for assessing
crop destruction from any natural or man-made disaster,"
said Mace Bentley, lead author of a study on the satellite
assessment technique.

The study is published on the cover of the March Bulletin
of the American Meteorological Society. Bentley is a meteorology
professor in the Department of Geography at Northern Illinois
University.

Bentley said imagery produced from the satellite data found
significant damage that went undetected by traditional means
of assessment. Bentley and University of Georgia researchers
Thomas Mote and Paporn Thebpanya used data produced by the
U.S. satellite known as Landsat 7, which acquires high-resolution
images of the earth's land surface.

Each year more than 20,000 thunderstorms erupt in the United
States, causing between $1 billion to $3 billion in property
and agricultural losses. Many of the most damaging thunderstorms
with extensive winds and hail are concentrated in the country's
central plains and Corn Belt regions and occur during the
late spring and summer months, the primary growing season.

"You're definitely going to see Landsat data used more
and more often to assess damage not only from thunderstorms
but also from tornadoes, brush fires and any other disaster
that destroys vegetation," Bentley said.

"Spatial mapping of agricultural damage could be used
by farmers, insurance companies and even meteorologists examining
storm formation and downburst potential," he added. "Combining
this technology with radar would help meteorologists identify
and be able to recognize storm features that produce the greatest
amounts of damage. As advances in satellite remote sensing
continue, there is also evidence that these techniques could
prove useful for damage assessment in urban and suburban areas
as well. Additionally, storm damage assessment using satellite
data gives us global coverage."

Bentley said the satellite-produced imagery has distinct
advantages over standard methods of storm-damage assessment,
which typically consist of drive-by observations or occasional
aerial photography. Those methods are particularly inadequate
when trying to estimate the number of acres damaged, Bentley
said. "Using data from the Landsat 7 represents a superior
method of identifying actual acres that sustain damage,"
he said.

Landsat 7 data can be used to measure differences in ground
reflectance among different land-surface types. The satellite
can detect chlorophyll absorption in vegetation and will identify
changes in ground reflectance once crops have been destroyed-or
within a week to 10 days after a storm, Bentley said. With
the launch of Landsat 7 in 1999, the cost of acquiring data
has dropped significantly, he added.

The researchers specifically examined two wind and hail storms
that rolled through a total of 14 counties in the corn- and
soybean-rich region of west-central Illinois on Aug. 12 and
Aug. 18 of 1999. The researchers compared data from July 12
(before the storms) and Aug. 28 (after the storms) to determine
damage extent.

The major storm on Aug. 12, destroyed thousands of acres
of corn across the area, causing more than $53 million in
crop damage in eight counties, according to estimates published
in Storm Data, a monthly publication produced by the National
Climatic Data Center. A second series of storms six days later
caused an additional $4 million in hail damage to corn and
soybeans.

In comparison, Landsat 7 data detected more than $100 million
in damage from the two storms. However, due to prevailing
soft-soil conditions and the ability of farmers to modify
harvesting equipment to salvage blown-down crops, actual losses
were only a fraction of that.

"Conditions were just right to make the crops salvageable,
something we couldn't determine from the satellite imagery
alone," Bentley said, adding that the case study points
to one limitation of using the satellite data.

"It's much easier to determine hail damage than wind
damage," he said. "That's not real surprising because
large hail pulverizes crops. Wind, on the other hand, may
simply blow the crops over. Sometimes portions remain rooted
and still survive, though less productive and more difficult
to harvest.

"Satellite images sometimes show a different picture
than the actual storm reports," Bentley added. "By
combining the old-fashioned methods of storm-damage assessment
with the high-tech imagery, we can get more accurate readings
of crop damage. And when we're talking about millions of dollars
in potential losses, that's good news for farmers and insurance
companies."